The present invention relates to a control gear for a fluorescent lamp, comprising a voltage source and an ignition and supply circuit comprising an inductive component and a capacitance.
Fluorescent lamps are generally used owing to their good lighting power. In addition, the long operating life of fluorescent lamps and the various tones of color available enable their use in various applications.
A control gear is required for burning fluorescent lamps, the control gear supplying the ignition voltage necessary for the fluorescent lamp and the supply voltage necessary during its use. When using electronic control gears, a problem arises from the fact that a lamp circuit has very high voltages which set extremely high demands on the switches used in the lamp circuit. Due to the high voltage levels, it is possible that the lamp ignites prematurely before the electrodes of the lamp are heated enough. This may lead to quick wear of the electrodes and uncertain ignition. In addition, in present prior art solutions, there are significant problems in the control of the switches in the lamp circuit and in determining the working condition of the lamp, which are due to said high voltage levels.
When a long ignition durability is required in fluorescent lamps, they should be ignited so that heating voltage is first switched on in the heater circuits for approximately one second so that they will reach the temperature required for a thermal electron emission. Only after this, an ignition voltage is switched on over the lamp, generating an arc discharge in the filler gas of the fluorescent lamp.
The above-mentioned function can also be performed by preventing the fluorescent lamp from igniting during preheating by short-circuiting it with a switch. The conventional use of a series choke and a glow discharge igniter in 50 Hz mains voltage use, for instance, is based on this method.
The problem in this case is that the used switch is greatly loaded due to the high voltages in the lamp circuit. Another drawback in the solution in question is that the switch over the lamp and its control electronics cannot be galvanically separated from the high-voltage lamp circuit.
It is an object of the present invention to provide a control gear for a fluorescent lamp, which avoids the above drawbacks and makes it possible to keep the fluorescent lamp unignited during preheating of the electrodes and to measure the voltage over the lamp with a simple apparatus while the lamp is operational. This object is achieved by a fluorescent lamp control gear of the invention, characterized in that the control gear also comprises a transformer whose primary coil is connected parallel to a capacitance, and a switching element which is connected to the secondary coil of the transformer for short-circuiting it.
The control gear of the invention is based on the idea that by adding to the lamp circuit a transformer connection whose secondary coil can be opened and shut with a switch, it is possible to ensure that the preheating of the fluorescent lamp is long enough. The transformer connection also makes it possible to monitor the condition of the fluorescent lamp in a simple manner by monitoring the magnitude of the voltage in the secondary coil of said transformer.
The fluorescent lamp control gear of the invention provides significant advantages with respect to the reliability of the lamp ignition, because the preheating of the fluorescent lamp is arranged by means of the control gear of the invention so that the lamp cannot ignite before the electrodes are heated. Another significant advantage provided by the control gear is the possibility to monitor the condition of the lamp by using simple voltage measurement from a voltage that is considerably lower than the actual voltage of the lamp circuit.